JP5876651B2 - Blunt metal powder or alloy powder and method and / or reaction vessel for producing the same - Google Patents

Description

  The present invention can be handled when exposed to air and has an average particle size of less than 10 μm (measured by a transmission method such as the Blaine or Fisher method), a passivated ultrafine elemental zirconium, titanium and / or hafnium Metal powders are produced by the metal thermal reduction of these oxides with calcium or magnesium, and are particularly suitable for the work, consisting of an evaporator crucible, an evaporator cover and an inner crucible, and a reduction reaction It relates to a reactor that makes it possible to add a phlegmatizing gas and / or a solid substance during and / or after.

  As blunting additives, inter alia hydrogen is used in an amount of 500 ppm or more, nitrogen is used in an amount of 1000 ppm or more; as blunting solid additives, carbon, silicon, boron, nickel, chromium and aluminum are used in an amount of 2000 ppm or more.

  The oxides can be reduced individually to produce pure metal powders, but the oxides can be mixed with each other or reduced in a mixture with metal powders and / or oxides of elemental nickel, chromium and aluminum. Thus, alloys of these elements with titanium, zirconium and hafnium can also be produced.

Principle of metal thermal reduction To obtain rare metals from their oxides, metal thermal reduction using calcium and magnesium as reducing agents is used in the following cases: for example, electrochemically from an aqueous solution or molten salt, Or when other methods cannot obtain rare metals, such as by reduction of these oxides with carbon or gas (eg hydrogen or carbon monoxide), or only with low purity. Typical industrial products in this regard are by using magnesium, calcium or aluminum to produce rare earth elements such as yttrium, cerium, lanthanum, and metal beryllium from these oxides or halides (Roempps). Chemical Dictionary: “Metal fever”). The metal thermal reaction is also used to obtain rare metals in a predetermined fine powder form that are usually used in powder metallurgy, pyrotechnics, or as getters for vacuum technology. The particle size of the metal powder thus produced can be largely determined in advance by selecting the particle size of the corresponding metal oxide to be reduced. (Petrikeev et al., Tsvetnye Met., Number 8 (1991) 71-72 (Non-patent Document 1))

Further, European Patent Application Publication No. 16454449 (US Patent Application Publication No. 2006/0174727) (Patent Document 1) includes metal powders of elements Ti, Zr, Hf, V, Nb, Ta and Cr, For example, a method for producing metal hydride powder, in which oxides of these elements are mixed with a reducing agent, and this mixture is heated in a furnace in a hydrogen atmosphere as necessary until a reduction reaction starts in a furnace. A method is described in which the product is leached and subsequently washed and dried, where the average particle size of the oxide used is 0.5-20 pm and the specific surface area by BET is 0.5-20 m ² / g. The minimum content is 94% by weight. This process does not describe a suitable reactor design.

  By mixing various reducing oxides, a powder-like alloy can be produced, for example, an alloy of Zr and Ti by mixing zirconium oxide with titanium oxide, or zirconium oxide with nickel and nickel oxide. And an alloy of zirconium and nickel can be produced. By mixing the reducing metal and suitably selecting the particle size of the reducing agent, the initiation of the reduction process and the reaction kinetics can be influenced. The heat of reaction depends on the oxide to be reduced, the reduced metal, and possible side reactions. The heat of reaction can be calculated according to thermodynamic principles using the free reaction enthalpy of the extract and product. In general, aluminum and magnesium have the strongest reducing effect following metallic calcium. When selecting a reducing agent, it should be taken into account that unless otherwise desired, any alloy with the rare earth metal obtained by reduction should not be formed. Also, the metal oxide of the reduced metal formed during the reduction must not form any double oxide or other mixed oxide with the oxide to be reduced, because this side reaction is not This is because the yield decreases as a result of the parallel occurrence.

  Since metal thermal reductions proceed most rapidly and vigorously with high reaction heat, the vapor pressure of the reduced metal is predicted (approximately 800-1400 ° C. in most cases) and the reaction temperature calculated as needed Should be considered in relation. Moreover, the reduced metal oxide formed during the reduction must be soluble in water or aqueous acid so that it can be removed from the reaction mass by leaching after the conversion is complete. The fact that silicon and aluminum oxides are sparingly soluble and that they tend to form mixed oxides is why these elements, which are themselves cost-effective, are less frequently used as reducing agents.

  In general, the metal thermal reduction reaction occurs automatically. These are understood to be reactions that are initiated by priming and continue automatically without the addition of external energy. Initiation can be initiated chemically, electrically (by hot wire or by induction), or simply by heating a portion of the metal / metal oxide-mixture in a predetermined manner (German patent invention) (DE PS) No. 96317 (Patent Document 2)). This is why it is also called hot spot ignition.

  As the reducing furnace, a gas combustion type crucible furnace or an electric heating furnace is suitable. In other respects, the design of the reduction furnace plays only a subordinate role. Theoretically, it is also possible to initiate the reaction by burning coal or burning coal in the evaporator. Gas fired crucible furnaces have the advantage of heating the evaporator quickly. Depending on the particle size and type of material used, an initiation occurs at a temperature of about 100-450 ° C., starting with one hot spot, often located in the lower third of the crucible containing the mixture to be converted. . When reducing Ti, Zr and Hf oxides, the temperature will later rise to a value between 900 ° C. and 1200 ° C. within a few minutes depending on whether calcium or magnesium is used as the main reducing metal. . Calcium provides temperatures above 1000 ° C. and magnesium provides a slightly lower maximum temperature. During heating, especially during the start of reduction, the pressure inside the evaporator rises. When a superatmospheric pressure of about 50-100 mbar is reached, the valve is released and releases superatmospheric pressure. In many cases, it is hydrogen that is formed by the moisture of the material used, the magnesium metal vapor, and the alkali metal vapor resulting from contamination of the material used. This can cause a flame at the release valve. The generated water vapor and dust must be sucked in at each generation position. The release of the valve can be done not only manually but also electromechanically or by compressed air, but for safety reasons it can also be remotely controlled, for example by video observation. As a superatmospheric pressure release valve, a plug valve is mainly used without using a gasket or a ball valve having a large cross-sectional area.

  Metallic thermal reduction continues spontaneously after igniting. The initiated reaction cannot be stopped by using conventional process techniques such as cooling or by adding diluent.

This means that the metal thermal reduction reaction resolutely requires special safety measures and a well-considered reactor design for:
Subject to a controlled atmosphere and control over a period of time to produce a reaction,
The ability to add a certain small amount of additional material to affect the properties of the rare metal via the gas phase during the reaction,
Control the reaction in such a way that the entire reaction does not explode, and produce a product that can be handled when exposed to air and is not pyrophoric.

  A step that is almost always required in the thermal metal reduction to produce reactive rare metals is to deactivate the reaction mass before, during, and after the reduction reaction. For this purpose, the reduction reaction is carried out under an inert protective gas, usually argon or helium. Alternatively, the reduction can be initiated and carried out in a vacuum.

  In Example (1), for example, even if metal thermal reduction of zirconium is carried out in a ceramic container exposed to air or under a slag blanket as in EP 0 586 670 A1 (Patent Document 3), The formed zirconium powder will recombine with oxygen in the air after the reaction while cooling the reaction mass. You will find a mixture of zirconium metal that is not fully reduced and mainly zirconium oxide. If the amount of metal obtained is small, it will not actually be useful. Similarly, this is true for titanium metal and hafnium.

  When producing highly reactive rare metals such as zirconium, titanium and hafnium, the metal powders can be blunted in the desired manner so that they can be handled even if they are later exposed to air and further processed. Need to be able to. Ultra-high purity titanium, zirconium and hafnium, which contain no gas or oxygen, are pyrophoric in their finest powder form, in other words, they ignite and burn instantly when in contact with air to form oxides. obtain. In the literature (Anderson, H. and Belz, L., J. Electrochem. Soc. 100 (1953) 240) (Non-Patent Document 2), the value below which dangerous pyrophoric zirconium powder is present is The average particle size when measured according to a transmission method such as Blaine or Fisher method is 10 μm.

  Gas-free ultra-pure zirconium, when present in its finest form, reacts with water under certain circumstances, similar to the known reaction of water with alkali metals that form hydrogen in explosive reactions. there is a possibility. Literature: Accident & Fire Protection Information, US Atomic Energy Commission Issue No. 44, June 20, 1956 (Non-Patent Literature 3) reports on this type of explosion.

  Titanium, zirconium and hafnium, and alloys of these metals are only stable in air because they are oxygen-impermeable oxide or oxide nitride covers, so-called passive layers, at room temperature. It is because it is surrounded by. Passivation is also known from many other metals, such as aluminum, zinc and chromium. For most metals, passivation occurs by itself. When the metal surface comes into contact with oxygen and nitrogen in the air along with moisture and carbon dioxide contained in the air, a protective passive film is formed without any special attempt. This is not true for metals Ti, Zr, and Hf and alloys when present in fine powder form and produced in a controlled atmosphere or under vacuum under argon, helium. In this case, the metal powder does not ignite spontaneously when removed from the controlled gas atmosphere, if the blunting material, in particular nitrogen and hydrogen gas, most often oxygen-containing gas, is also added as desired, or As mentioned above, it will surely react explosively when in contact with water.

European Patent Application No. 16454449 (US2006 / 0174727) German Patent Invention (DE PS) No. 96317 European Patent Application No. 0583670A1

Petrikeev et al., Tsvetnye Met., Number 8 (1991) 71-72. Anderson, H. and Belz, L., J. Electrochem. Soc. 100 (1953) p. 240 Accident & Fire Protection Information, US Atomic Energy Commission Issue No. 44, June 20, 1956 J. Fitzwilliam et al., J. Chem. Phys. 9 (1941) 678 J.D.Fast, (Metal Processing) Metallwirtschaft 17 (1938) 641-644 Berger, B., Gyseler, J., Method of testing the sensitivity of explosives with respect to electrostatic discharge (Methode zur Pruefung der Empfindlichkeit von Explosivstoffen gegen elektrostatische Entladung), Techn. Of Energetic Metals, 18th Ann. Conf. Of ICT, Karlsruhe 1987, 55 / 1-55 / 14

  The object of the present invention is to provide a method for producing a metal powder or alloy powder of the reactive metal zirconium, titanium or hafnium from the corresponding oxide or oxide mixture, and a reaction vessel for carrying out the method. It is provided that the resulting reactive metal powder or alloy powder can be handled later when exposed to air, for example, for further processing.

To solve the above problem, a metal powder or alloy powder having an average particle size of less than 10 μm and comprising or containing at least one of the reactive metals zirconium, titanium, and hafnium is converted into the reactive metal with the aid of a reducing metal. A method for producing a metal powder or an alloy powder by metal thermal reduction of an oxide or halide of
Blunting by adding a passivating gas or gas mixture during and / or after the reduction of the oxide or halide and / or by adding a passivating solid material before the reduction of the oxide or halide This was solved by a method of carrying out reduction and blunting in one gastight and evacuable reactor.

  The process is carried out in accordance with the present invention in a suitable reactor described in more detail below.

  On the one hand, the method and the reaction vessel according to the present invention allow the reduction reaction to be carried out under an inert gas such as argon or helium or in vacuum, eliminating the uncontrolled access of air and moisture. In particular, this design allows a certain amount of gas to be added as desired during and / or after the reduction reaction to blunt the metal or alloy formed in the desired manner and affect their chemical behavior. It becomes possible. This design further enables the reduction of oxides or oxide mixtures under a reactive gas atmosphere, in particular under hydrogen, when the production of hydrides of metals Ti, Zr and Hf is intended. Heating and addition of hydrogen also allows hydrogenation of alloys produced by melt metallurgy, such as alloys of 70% Zr and 30% nickel or alloys made of sponge titanium. In addition to hydrogen, ammonia, methane, carbon monoxide, carbon dioxide and nitrogen are fed into the evaporator to hydride, sub-hydride, carbide, nitride, hydride of metallic zirconium, titanium and hafnium. -Nitride mixtures or oxynitrides can be produced. This configuration includes a special design that cools the flange and cover to prevent cooling water from entering the evaporator unnecessarily. Certain spacer assemblies with support rings allow the evaporator to be installed at various depths in the combustion space of the reduction furnace.

  The reduced metal used here is preferably calcium and / or magnesium. Therefore, calcium and magnesium can be used alone or in combination. In principle, further additives such as carbon, silicon or silicon oxide and other substances can be added to influence the properties of the reactive metal powder produced in the reduction.

  Preferably, nitrogen and / or hydrogen is added as a passivating gas. Here, in order to avoid the above reaction, the metal powder should contain 500 ppm or more of hydrogen and 1000 ppm of nitrogen. For safety reasons, the amount of hydrogen should be greater than 1000 ppm (0.1%) in the best case, preferably 1000-2000 ppm, and the amount of nitrogen is 2000 ppm (.0. 2%) or more, preferably 2000 to 3000 ppm. Nitrogen and hydrogen may be added in the form of ammonia.

  As passivating solid material, carbon, silicon, boron, nickel, chromium and / or aluminum of 2000 ppm (0.2 wt%) or more and 30,000 ppm (3 wt%) or less can be added. The passivated solid material can also be reduced together with the metal oxide in the form of fine oxides of the elements Ni, Cr, Al, Si and B having an average particle size of less than 20 μm. Alternatively, a passivated solid material in the form of a fine powder of the element Ni, Cr, Al, Si, B or C having an average particle size of less than 20 μm can be added. According to a further variation of the method embodiment, carbon can be added via the gas phase in the form of methane, carbon dioxide or carbon monoxide. Eventually, the passivating gas and the solid material can also be added together.

  The flammability of the blunted metal powder or alloy powder can be further reduced by washing out submicron particles with a particle size of less than 0.2 μm during leaching and / or washing.

The mechanism and / or reason for this slowing is not precisely known. Although speculation is possible, it does not necessarily result from “forming a layer” of metal hydride or metal nitride on the particle surface with a small amount of gas. When the final porosity is tied to the large specific surface area of the metal powder, there is a certain minimum amount of N and H required to ensure at least a monomolecular cover of the metal surface. On the other hand, the metals Ti, Zr and Hf have a considerable solubility in the gas. For example, in a zirconium metal matrix, 5% hydrogen and up to 20% nitrogen can be present in a solid solution (J. Fitzwilliam et al., J. Chem. Phys. 9 (1941) 678) (non-patent literature). 4). Regarding titanium, it is mentioned that the atmospheric pressure of hydrogen is 7.9% and the atmospheric pressure of nitrogen is 18.5% (JDFast, (Metal Processing) Metallwirtschaft 17 (1938) 641-644). (Non-patent document 5). Therefore, it is probably not certain that TiH ₂ , ZrH ₂ , ZrN is phased or compounded on the surface, because in such cases the solubility limit must be exceeded. .

  One hypothetical concept by the inventor is as follows: free electrons in the metal so that by placing the gas in the metal matrix, no spontaneous reaction with oxygen or reaction with water due to combustion occurs. Reduce the total energy level of In the following wet chemical treatment of metal powders in water and acids, only the actual oxide passivation layer is formed on the particle surface due to the slow oxidation reaction with oxygen in the air and / or the slow reaction with water. The When the metal powder is heated to just room temperature or at most the boiling point of water in wet chemical processing, the entire diffusion process is slow, in fact, where the dense, solid metal oxide (and metal nitride) A “passive layer” can be formed that adheres to the metal, which permanently protects the metal from further oxidation. This assumption is verified by experiments conducted by the inventor. Further details of the experiment are not described here, but during the treatment of weakly oxidizing substances (eg hydrogen peroxide, hypochlorite, alkali nitrite) or layer-forming substances (eg phosphoric acid) phosphate and chromium The acid salt was added to promote the passivation of the metal powder. This assumption is also proved in practice by the fact that slight gas formation (hydrogen) can always be observed in the form of minimal bubbles during processing of metal powders in acid and later in water. Exit after time has passed. It should also be noted that the analyzed hydrogen content in the metal powder is always higher than the theoretically calculated value based on the addition of hydrogen. Thus, the metal also absorbs hydrogen again during the wet chemical process and finds its source in the decomposition of excess reducing agent (Mg, Ca) and also in the reaction that takes place in the face between the metal and water. be able to.

  According to the present invention, the effect of placing the gas on the metal matrix is particularly useful. Such an arrangement is particularly advantageously achieved by the fact that the blunting compound has already been added during the reduction reaction. Quantifying the degree of passivation is difficult and can best be determined from the flash point of the metal powder exposed to air. Various standard methods are sometimes available to measure the flash point of a solid material. For the metals Ti, Zr and Hf, the following simple test arrangement is preferred: a hole with a diameter of 15 mm and a depth of 35 mm is drilled in the center in a copper or steel cylinder with a diameter and height of 70 mm. At 5 mm intervals, a 5 mm wide hole with a depth of 35 mm is drilled, which serves to accommodate the thermocouple element. Preheat the block uniformly to about 140-150 ° C., then inject an amount of 1-2 g of the metal powder to be tested into the larger perforation and continue heating until ignited, which is optical (eg by a video camera) Can be recognized. By analyzing the time / temperature curve of the temperature sensor, the flash point can be determined fairly accurately. If the flash point is less than 150 ° C., safe passivation or blunting cannot be assumed. Metal powder with such a low flash point should be destroyed by combustion at the storage site.

  The combustion time gives a reference point for the degree of bluntness. The method is described in Example 1. It is mentioned that the dullness reference point is very difficult to measure, but can also be obtained from a measurement of electrical minimum flammability energy (Berger, B., Gyseler, J., Method of testing the sensitivity of explosives with respect to electrostatic discharge (Methode zur Pruefung der Empfindlichkeit von Explosivstoffen gegen elektrostatische Entladung), Techn. of Energetic Metals, 18th Ann. Conf. of ICT, Karlsruhe 1987, 55 / 1-55 / 14) (non-patent literature) 6).

  In the present invention, the metal powders of Ti, Zr and Hf and the alloy powders of these metals and Ni, Cr and Al are blunted by adding a certain amount of hydrogen and / or nitrogen in an exhaustable hermetic evaporator. Occurs during and / or after the reduction. Some of these gases may be present in the evaporator from the beginning. Better and more precisely, after reaching the maximum temperature, a passivating gas may be added to the reactor (evaporator) while cooling the fully reacted mass.

  The elements Ni, Cr and Al have two functions and can be used to produce alloys of Ti, Zr and Hf, as well as blunt addition fixed to pure metals in small amounts of 2000 ppm to 3% Acts as a thing.

  Also, non-metal additives such as carbon, silicon, boron, or metal additives such as iron, nickel, chromium, aluminum, etc. can affect the reactivity of zirconium, titanium and hafnium to water, air and oxidants. Can do. Addition of silicon or boron generally reduces the burning rate slightly but can increase the ignition temperature. Rather, a negative example is iron. Iron additives tend to provide thermal spray sparks, lower the flammability temperature of zirconium metal, and in most cases increase the flammability with respect to friction. Carbon can be added to the evaporator according to the present invention by adding a certain amount of carbon dioxide or methane. In general, carbon causes a slowdown. The other elements are best added to the starting mixture in the form of oxides or directly in the form of elements as a powder. However, the addition of solid materials in small amounts is not due to inadequate mixing or due to segregation, so that all metal particles do not come into contact with the additive and in addition to the injected blunt metal particles, This leads to the problem that particles other than the alloy exist. The latter can ignite during processing, resulting in combustion of the entire starting mixture. In contrast, the gaseous additive is itself uniformly distributed throughout the evaporator chamber and generally reaches all the metal particles formed. For this reason, work with gaseous additives is mainly recommended.

  According to the present invention, the blunting of titanium, zirconium and hafnium metal powders or their alloy powders with gas can be realized on an industrial scale by using a specific reaction vessel (evaporator). According to the above method, a blunted metal powder or alloy powder having an average particle size of less than 10 μm and comprising or containing at least one of the reactive metals zirconium, titanium or hafnium is obtained with the aid of a reducing metal. The reactor according to the invention for producing by metal-thermal reduction of reactive metal oxides or halides can be inserted into a heatable reduction furnace and has an evaporator crucible with a coolable cover; An inner crucible, the coolable cover having at least one inlet for introducing a passivating gas or solid material, on the lower surface of which the cooler is welded to the evaporator cover to place the coolant The flange is welded to the evaporator crucible. Instead of this welded connection, other suitable types of connections are within the scope of the present invention.

In the literature describing the metal thermal reduction reaction, it is often mentioned only that the reaction is carried out in a closed steel evaporator under inert gas, with no details on the design features of the evaporator. The description is not given. Often mention is made of steel evaporators which are bolted together, i.e. so-called cylinder tubes which do not have any openings and connect at best a manometer. These types of structures are based on inert gas (Ar, He), reactive gas (H ₂ , CO, CO ₂ , NH ₃ , CH ₄ ) or solid addition to the extent that the evaporator chamber can be emptied prior to the reaction. things _{(Ni, NiO, Cr, Cr} 2 O 3, C, Si, SiO 2, B, B 2 O 3) but allows the addition of, not the possible during and after reduction. This type of evaporator is definitely suitable for scientifically measuring the characteristics of rare metals, but not suitable for producing large amounts of rare metals in a short time. When the reaction vessel is tightly locked, important properties in pyrotechnic and getter technology, such as burning rate, flash point and bluntness cannot be adjusted in the desired manner. It should be noted that since there is often no useful information about the dominant pressure, opening the locked steel evaporator after the reaction has taken place is not without danger. Uncooled evaporators require a refractory metal or ceramic gasket (copper, silver or refractory fiber) between the cover and the evaporator crucible and can be used only once in most cases. Also, large evaporators can only be sealed with difficulty in this way, and such gaskets only allow the use of small evaporators in quantities in the sub-kilogram range. According to an advantageous embodiment of the reactor, the cooler is fitted with a gasket extending annularly under the flange, which is not connected to the actual evaporator crucible.

  Any other coolant may be used as an alternative to water for cooling at the crucible flange and / or for cooling the cover. Thus, for example, organic heat transfer media such as heat transfer oil, preferably silicone oil, or air can be used. A suitable silicone oil can be purchased, for example, as Therminol® VP from Solutia GmbH. The coolant circulates in a common or independent suitable cooling cycle.

In addition to the inlet for introducing the passivating gas or solid substance, the coolable cover further comprises at least one connection for a vacuum pump. In addition, the cover can have the following connections: a connection with a heat-resistant gasketless ball valve or plug valve to release superatmospheric pressure, a connection for a vacuum pump to empty the evaporator Part, inlet for introducing an inert gas such as argon from the tube, inlet for introducing a reactive gas such as H ₂ or N ₂ from the tube, connection holding a safety valve, vacuum or pressure measuring device Connection and connection for one or more temperature sensors (Pt / RhPt). Where appropriate, grooves for gasket rings, preferably made of Viton, can be provided in the cover to the extent that they are not present in the evaporator crucible. For example, water cooling can be designed on the cover as an annular channel. The cover can preferably be connected to the flange by a screw connection.

  Furthermore, it is particularly important that the cooling of the evaporator cover is not connected to the inlets and through fittings of the cover plate. Thus, in particular, the flange cooler must not have a connection to the evaporator crucible and must open towards the evaporator wall.

  Further advantages and specialities of the process according to the invention and the reaction vessel for carrying out the metal thermal reduction to obtain metallic zirconium, titanium, hafnium and their alloys and other rare metals in a finely powdered blunt form, The following non-limiting embodiments are illustrated in conjunction with the drawings.

1 shows a reduction furnace with a reaction vessel for performing metal thermal reduction to obtain metallic zirconium, titanium, hafnium and their alloys, and other rare metals. Evaporator crucible is shown. Figure 3 shows a cooled evaporator cover. Figure 3 shows a spacer assembly. Show the inner crucible.

  According to FIGS. 1 and 2, the evaporator crucible 1 is made of heat-resistant steel 1.4841 or equivalent steel, can withstand temperatures up to 1300-1400 ° C. for a short period of time, and preferably has an inner diameter Di = 500 mm . The wall thickness is 10 mm or more, preferably 15 mm. The flange 2 having a material thickness of 30 mm and a ring width of 150 mm is welded to the evaporator crucible 1, and a cooler 3 for cooling water is welded to the flange 2. The flange 2 is also preferably made of heat resistant steel 1.4841 or equivalent steel. The decisive design features are as follows: the cooler 3 is exactly located under the gasket 4 which extends annularly under the flange 2 and this cooler 3 is connected to the actual evaporator crucible 1 There are no connections. The flange 2 allows for the installation of the cover 5 between the cover and the evaporator crucible using a gasket ring 4 made of Viton, Perbunan, Teflon or a different general sealing material between the cover 5 and the flange 2. Allows air-tight and vacuum-tight connection. The gasket ring 4 may be set to a groove milled in the flange. Furthermore, a support ring with a spacer bracket 20 can be screwed into the crucible flange 2 so that the evaporator can be inserted into the furnace space and / or the combustion chamber 18 of the reduction furnace 17 that can be heated at various depths. The reduction furnace 17 can be heated preferably with the aid of an electric heater 16.1, or alternatively a gas heater 16.2.

According to FIG. 3, the coolable cover assembly has the following design features:
Cover 5 made of heat-resistant steel 1.4841 or an equivalent material having a thickness of 25 mm or more, preferably 30 mm,
An inlet 12 with a heat-resistant gasketless ball valve or plug valve for releasing superatmospheric pressure,
An inlet 13 for connecting a vacuum pump for emptying the evaporator,
Inlet 7 for introducing an inert gas such as argon from the feed,
An inlet 8 for introducing a reactive gas such as H ₂ or N ₂ from the feed,
Connection 9 with safety valve (p = 0.25 bar),
Connection port 11 (0.1 to 1,500 mbar) for connection to a vacuum or pressure measuring device (manometer),
Connection 10 for inserting one or several temperature sensors (Pt / RhPt),
Optional groove for holding the water cooling system 6 and preferably the gasket ring made of Viton to the extent that it is not provided in the evaporator crucible. For example, the water cooler 6 can be designed as an annular channel on the cover 5. The cover 5 can be preferably connected to the flange 2 by means of screws 19.

  According to FIG. 4, a spacer assembly 20 with a support ring is provided between the flange 2 and the heatable reduction furnace 17.

  According to FIG. 5, the inner crucible 14 contains the starting mixture 15, ie the mixture of the metal oxide to be reduced and the reduced metal. Depending on purity requirements, the inner crucible 14 is made of structural steel, heat resistant steel or stainless steel, preferably St37 or VA, having a thickness of 2-5 mm, preferably 2-4 mm. The inner crucible 14 holds the reaction mass removed from the actual evaporator and serves only as a “receiving vessel” during the reduction reaction. After cooling, the inner crucible can be removed from the evaporator and optionally stored in a different container under inert gas, for example a stainless steel drum, until the contained reduced mass is processed. . A protective tube 21 can be inserted into the initial mixture 15 to hold one or several temperature sensors.

  A special feature of the present invention is that it is designed to cool the reduction evaporator cover 5 and flange 2. The cover 5 and the evaporator crucible 1 are connected in a gas-tight and vacuum-tight manner by a gasket 4 made of Viton, Perbunan, Teflon or other conventional sealing material. The gasket 4 can be designed as a flat ring or an O-ring. The gasket 4 must be cooled because it may otherwise decompose at high reaction temperatures. In this variant of the embodiment, the cooling is performed with water. If water enters the evaporator chamber through cracks or corrosion holes during the reduction reaction, it becomes devastating. This leads to intense hydrogen formation and explosion in the evaporator. Cooling design is therefore an important feature of the reactor. The crucible flange cooler 3 is fitted on the bottom surface of the flange 2 and has only one connection on the flange itself, but not on the evaporator wall. Thus, water must not enter the evaporator from this area. The cover 5 is cooled only on the surface of the cover 5, but does not have a connection portion to the inlet and the through attachment portion. In order for the cooling water to reach the inside of the evaporator, the heat-resistant steel having a wall thickness of 30 mm or more is unlikely to be applied at all, and the cooling water must pass through the huge cover 5. FIG. 3 shows the cooling as water cooling 6 in more detail.

  The evaporator crucible and the evaporator cover are connected by a suitable number of screws and nuts 19. The evaporator made up of the evaporator cover 5 and the evaporator crucible 1 is used directly to immediately accommodate the different inner crucible containing the new starting mixture after the inner crucible 14 containing the reacted blunted mass has been removed. be able to. In this way, several evaporators can be subjected to the reaction from one to the next in one furnace.

  The dimensions shown in the figure are suitable for an evaporator for carrying out the example, ie to obtain about 25 kg of metal powder / starting mixture.

Example 1
An example of metal thermal reduction using the above principles and the present invention is to obtain zirconium in powder form by reducing zirconium oxide with calcium, and for getter technology (lamp, vacuum parts) and military pyrotechnic technology, eg thermal battery To apply to the generation.

  Zirconium oxide having an average particle size of 5 ± 0.5 μm measured by the Blaine method or the Fisher sub-sieve sizer method is mixed with calcium chips or granular metal having a particle size of 0.5 to 5 mm. To do. Calcium metal is added in the stoichiometrically required stoichiometric amount. In order to control the reduction reaction, a small amount, for example 2 to 10% by weight, of the theoretically required stoichiometric amount of magnesium chips having the same size as the calcium chips is also added. In principle, the addition of further additives, mostly carbon, silicon or silicon oxides and other substances, can affect the properties of the zirconium powder produced during the reduction. In isolated zirconium powders in the range of 500 to about 5000 ppm, the amount of gaseous additive is measured by the method as shown below when the solid material as ("contamination") is greater than 2000 and less than 3%. . In this example, a small amount of silicon oxide is used that reappears as Si contamination in the isolated zirconium powder. The mixing of the components takes place under argon in a gyro wheel mixer, winding mixer or other equivalent mixing engine for solid materials. All ingredients must be kept strictly dry. By adding a small amount of the second reducing metal (magnesium), the initial flammability threshold is lowered, so that the reaction mixture can be ignited more easily than when only calcium is used. Because magnesium evaporates faster than calcium, heat is removed from the reaction mass as a result of the evaporation of magnesium, limiting the maximum temperature of the reaction mass.

  Alternatively, 3-15% by weight calcium oxide (unhydrated lime) or unsintered magnesium oxide can be added to dilute the reaction mass, reduce the reaction rate, and reduce the maximum temperature of the reaction. I can also do it. However, since this method is almost always used at the expense of the purity of the zirconium powder to be obtained, in this example, the work by adding magnesium is better.

component:
Zirconium oxide (average particle size 4.5 to 5.5 μm) 36.0 kg
Calcium (granular metal, minimum 99.7%, 0.5-5mm) 26.5kg
Magnesium (chip) 1.5kg
Silicon oxide 0.1kg (= 46gSi → 1840ppm)
Titanium oxide 0.05kg (= 30gTi → 1200ppm)

  The ingredients are weighed and thoroughly mixed in a drum mixer under an Ar atmosphere, then charged into the inner crucible and stored dry in an argon atmosphere until used in a reduction evaporator according to the present invention.

To carry out the reduction reaction, the inner crucible containing the mixture of the above components is inserted into the evaporator crucible according to the invention, the evaporator is locked by closing the cover, and the entire evaporator is pumped twice to finish The pressure is reduced to less than 1 mbar, air and any moisture present are removed and filled with argon. At least one temperature sensor is inserted and the temperature is measured in the reaction space by one of the through attachments. Connect a manometer that exhibits a value lower than atmospheric pressure of at least 0.1 mbar as well as superatmospheric pressure up to +1000 mbar. A connection is established with a gas pressure cylinder containing argon, nitrogen and hydrogen. The gas pressure cylinder is equipped with an accurate pressure reducer with a maximum pressure set at 100 mbar. Pre-measured amounts of these gases are filled into pressure cylinders for nitrogen and hydrogen. The inert gas argon needs to be always available with a sufficient remaining amount. Subsequently, the reduction is started by heating the evaporator in a gas-fired crucible furnace. After about 45 minutes, the metal thermal reduction reaction begins:
ZrO ₂ + 2Ca → 2CaO + Zr
In parallel, ZrO ₂ + 2Mg → 2MgO + Zr.

  In this example, the reaction starts at a temperature of about 100-140 ° C. and reaches 1100 ° C. within 2 minutes. After exceeding the maximum temperature (which can be recognized by the decrease in temperature measured by the temperature sensor in the reaction chamber), add the amount of gas necessary to blunt the zirconium powder and / or to set the combustion and flammability characteristics To do. In this example, 50 L of nitrogen and 130 L of hydrogen are added from the connected pressurized gas cylinder during the cooling phase. This corresponds to a hydrogen content of 500 ppm and a nitrogen content of 2500 ppm in the zirconium metal powder produced. These gases are rapidly absorbed by the zirconium metal during the cooling phase. Once all the gas has been added, the necessary pressure equalization occurs during the cooling process by the addition of argon. After the evaporator is cooled to about 600 ° C. in a powered off furnace, the evaporator can be removed from the reduction furnace, placed on a cooling frame, and cooled to room temperature by further adding argon. The reduction furnace can then be released and used during this time to heat and ignite the additional reaction mixture prepared in the second evaporator according to the invention.

After cooling is complete, the inner crucible containing the reaction vessel is removed from the evaporator, the reaction mass is removed, crushed with a jaw crusher, and leached into hydrochloric acid. Thereby, magnesium oxide and calcium oxide are converted into the corresponding chlorides and washed out. A fine zirconium metal powder metal sludge remains, the particle size approximately corresponding to the particle size of the zirconium oxide used, ie 5 ± 1 μm as measured according to Blaine or Fisher. The metal powder is washed, wet filtered (<45 μm) and carefully dried (<80 ° C.). Treating the metal powder in water and in an acid without adding any danger and causing a reaction with water due to the addition of added additives (here SiO ₂ ) and gas, here N ₂ and hydrogen Can later be exposed to the air without any spontaneous ignition. Yield is 25-26 kg (fine gray zirconium metal powder).

The burning rate of the metal powder thus obtained is measured as follows: a continuous rectangular groove having a depth of 2 mm and a width of 3 mm is milled in a steel block having a length of 60 cm, a height of 1 cm and a width of 4 cm. To do. The groove is filled with 15 g of the metal powder to be tested, the powder filling is ignited at one end, and the time required for the combustion front to travel a marked strip with a distance of 500 mm is measured. In this case, the burning rate is 80 ± 10 s / 50 cm. The ignition temperature is 240 ± 20 ° C. The electrical energy for ignition is about 18 μJ. By absorbing more hydrogen during the aqueous treatment, a total of 2000 ppm hydrogen is found in the final product. The metal powder also contains reduced metal contamination. However, these are generally small amounts. The amount of silicon found is 1800 ppm, the amount of nitrogen is 2500 ppm and the amount of titanium is 1000 ppm, which corresponds exactly to the theoretical amount.
Example 2

  The procedure of Example (1) is modified so that the evaporator containing the reaction mass is left in the reduction furnace after the reduction reaction has occurred. Additional external heat affects the rare metal particle size and / or combustion and chemical properties. When heated at about 900 ° C. for several hours, a sintering effect can be achieved, thereby coarsening the grain size of the resulting zirconium metal. In this example, by heating for 3 to 4 hours, the average particle diameter of zirconium metal can be increased from about 5 μm to 6 to 7 μm, and the combustion rate can be reduced from about 75 s / 50 cm to 100 to 120 s / 50 cm.

In this procedure, the flash point of the metal still remains almost unchanged and is 250 ° C. ± 20 ° C.
Example 3

The process described in Example (1) is used to produce zirconium metal suitable for use in the ignition system of air bag initiators and military explosives. However, the following are used as input materials:
Zirconium oxide (average particle size 1.5 / −0.25 / + 0.5 μm) 36.0 kg
17.1 kg of magnesium (chip, mineral 99.8%, bulk density 0.45 g / cm ³ )
Silicon oxide 0.35kg

The input material is mixed as in example (1), the inner crucible is filled and inserted into the evaporator. Unlike example (1), the evaporator is pumped twice, followed by 100 L hydrogen, 50 L nitrogen, and the remainder filled with argon. After heating, according to the following formula, when the temperature reaches 150 ° C. ± 20 ° C., the reduction reaction starts and reaches a maximum value of 960-1050 ° C.
ZrO ₂ + 2Mg → 2MgO + Zr

  In the cooling phase, 150 L of hydrogen and 50 L of nitrogen are added again to blunt the zirconium metal powder. A final pressure equalization is performed using argon during cooling. After removing the cooled reaction mass, it is leached into hydrochloric acid, washed, wet filtered at 45 μm and dried to obtain an ultrafine, highly flammable metal powder that has been blunted. Therefore, it does not ignite automatically when exposed to air. During washing, decantation is performed several times to remove the finest suspended metal particles with a particle size of less than 0.2 μm. The yield is about 25 kg. At temperatures below 70 ° C., the metal powder can be carefully dried.

  Combustion speed in the groove (compared with the example (1) exposed to air) is 10 ± 3 s / 50 cm. The average particle size of the metal powder is 1.7 ± 0.3 μm. The flash point is 180 ± 10 ° C. The minimum electrical ignition energy was measured to be about 2 μJ.

  The silicon content generally corresponds to the amount used and is 5900 ppm (theoretically 6530 ppm). The hydrogen content in the final product is 1400 ppm (theoretically 900 ppm) as it absorbs more water during acid leaching. The nitrogen content in the final product is 4000 ppm (theoretically 5000 ppm).

The high flammability of the metal powder is due to the high fine particle size and high sensitivity to charging. Generally, these metal powders are not dry, but are stored and carried in a suspension of 30% or more water by weight.
Example 4

Formation of Zr / Ni alloy The procedure of Example (1) is used, but without adding SiO ₂ and TiO ₂ :
Zirconium oxide (average particle size 4.5 μm) 36.0 kg
Calcium-granular metal 26.5kg
Magnesium (chip) 1.5kg

  The reaction occurs as in Example (1), but after pumping, the evaporator is not filled with argon, but is charged with 100 L of nitrogen (99.995). The reaction is initiated by heating. In this case, the reaction starts already at 80-100 ° C. and reaches a maximum value of about 1050 ° C.

  During cooling, an additional 100 L of nitrogen is added into the evaporator to slow down the zirconium metal and further pressure equalization is performed using argon.

  After the cooling is completed, the reaction mass is taken out and crushed but not leached. Instead, it is finely pulverized in an anhydrous argon atmosphere until the particle size becomes 150 μm. Note that 12 kg of nickel powder (average particle size of 5 μm by Fischer) is added to the metal mass containing Zr metal, calcium oxide and magnesium oxide, and excess magnesium and calcium (Ni powder is carcinogenic) ) Mix in a drum mixer in an argon atmosphere. The mass is then filled into an inner crucible, inserted into an evaporator according to the invention, evacuated and slowly heated in an argon atmosphere to limit the furnace temperature to 860 ° C. After about 1 hour, the furnace temperature is reached and only the internal temperature measured in the reaction mixture begins to rise after about 3-5 hours. Within 15 minutes, the temperature then increases from about 400 ° C to 880-900 ° C. As soon as the reaction starts, turn off the heating. In the reaction, the excess reducing agent still contained in the Zr reducing mass reduces the nickel oxide always contained in the nickel powder to Ni, and at the same time the Zr powder is combined with the nickel, A Zr—Ni alloy having a composition consisting of Zr and 30% by weight of nickel is obtained. In the cooling phase, 200 L of hydrogen is added.

  The reaction mass is left overnight in the evaporator by adding argon in a cooling frame. After release, the mass is removed, crushed and leached in acid to wash out calcium oxide and magnesium oxide. In this case, since the ZrNi alloy can be corroded by pure hydrochloric acid, leaching must be carried out in strongly acetate buffered hydrochloric acid. The Zr / Ni alloy remaining in the suspension is wet filtered (<45 μm) and dried.

  The resulting Zr—Ni alloy powder has a particle size of 4-6 μm as measured according to Blaine or Fisher. The yield is about 36 kg. The combustion time is 200 ± 30 s / 50 cm when measured in the combustion groove described in Example (1). The flash point is 260-280 ° C., and the hydrogen content is 0.2% (2000 ppm) with respect to the theoretical value of 500 ppm. Here, it is also shown that hydrogen is generated during chemical treatment in acid and absorbed by the metal. The nitrogen content was not measured but is theoretically about 1% (10,000 ppm). The electrical minimum igniting energy was found to be about 100 μJ.

  The alloy powder is suitable for the production of delayed initiators in accordance with US standard MIL-Z-114108.

Other Information The zirconium metal powder produced in the described example is blunted according to the present invention and does not spontaneously ignite spontaneously, ie can be exposed to air. By washing out sub-micron particles having a particle size of less than 0.2 μm, the flammability can be further reduced, usually by decanting during leaching and washing. The aqueous process itself contributes to the passivation of the metal surface. However, the aqueous process can also cause Zr, Ti and Hf metal powders to be surrounded by a thin oxide film and consequently charged. Thus, spontaneous ignition based on electrostatic discharge can occur without being based on “conventional” self-flammability. Therefore, Zr, Ti and hafnium metal powders must always be handled in a grounded metal container as much as possible and treated under argon whenever possible. When reproducing the examples described in the present invention, corresponding safety measures should be implemented and expert advice should be obtained from trained safety professionals.

1 Evaporator crucible 2 Flange 3 Cooling at crucible flange 4 Gasket (O-ring or flat band)
5 Cover 6 Water cooling 7 Inert gas inlet (Argon connection)
8 Inlet for H ₂ , N ₂ and other reactive gases 9 Connection 10 holding a safety valve Connection 11 with one or more temperature sensors Connection 11 for vacuum devices and pressure sensors (manometers) Pressure release Connection 13 for valve (ball valve or plug valve without gasket) Connection 14 for vacuum pump Inner crucible 15 Starting mixture 16.1 Heater (electric)
16.2 Heater (gas)
17 Heatable reduction furnace 18 Furnace / combustion chamber 19 Screw connection 20 Spacer assembly 21 with support ring Protection tube for temperature sensor

Claims (3)

A blunted metal powder or alloy powder with an average particle size of less than 10 μm and consisting of or containing the reactive metal zirconium is produced by metal thermal reduction of the reactive metal oxide with the aid of a reducing metal A method wherein the metal powder or alloy powder is
Nitrogen gas and hydrogen gas are added during and / or after the reduction of the oxide, and nitrogen is added to the metal powder or alloy powder as a passivating gas in an amount of 1000 ppm to 10000 ppm and hydrogen in an amount of 500 to 2000 ppm. Is slowed down by
A method characterized in that reduction and blunting are carried out in a single gas-tight reactor that can be evacuated.   The process according to claim 1, characterized in that nitrogen is added as a passivating gas to the metal powder or alloy powder in an amount of 2000 to 3000 ppm. It is further slowed down by adding 2000 ppm (0.2 wt%) or more and 30,000 ppm (3 wt%) or less of the passivated solid material before the reduction of the oxide,
The passivating solid material is selected from carbon, silicon, boron, nickel, chromium or aluminum;
The passivated solid material is added in the form of a fine oxide of elemental Ni, Cr, Al, Si or B having an average particle size of less than 20 μm and reduced with the metal oxide; and / or
3. The passivating solid material according to claim 1 or 2, characterized in that it is added in the form of a fine powder of the elements Ni, Cr, Al, Si, B or C having an average particle size of less than 20 μm. The method described.

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